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2.6.4 Environmental Factors
Avoid installing sensors where they are exposed to wind, dust, water, shock, or vibration.
Observe the temperature range limitations of sensors (Section 7.4.2).
2.6.5 Catalytic Poisons
Sensors are adversely affected by prolonged exposure t o c ertai n m aterials. Loss of
sensitivity (i.e. reduced response to combustible gases), or corrosion, may be gradual if
such materials are present in low concentrations, or it may be rapid at high
concentrations. The more important materials adversely affecting sensors are:
• Halides (compounds containing chlorine, fluorine, bromine, or iodine).
• Sulf ur compounds such as SO
2
(Sulfur Dioxide), H
2
S (Hydrogen Sulf ide), CS
2
(Carbon Disulfide).
• Heavy metals such as tetraethyl lead.
• Silicones (often contained in greases and aerosols). Silicones do not chemically
attack the sensor. They, instead, coat the beads and, therefore, reduce or stop
the oxidation of the combustible gas at the catalytically active bead.
• Acid vapors.
• Caustic liquids or vapors.
The presence of such materials in an area does not necessarily prec lude t he us e of a
catalytic bead sensor. The f easibility of using a sensor in such areas must be determined
by an analysis of the specific factors in each application. However, sensors used in s uch
areas usually require calibration checks on a more f requent basis and t ypically have a
shorter life than normal. In many such applications, the normal two-year warranty does
not apply.
CAUTION: General Monitors discourages the painting of sensor ass emblies f or t wo
reasons. First, if the sensor head is painted-over, gas will not be able to
dif fuse into the sensor. Second, many paints contain lead, which can poison
a sensor.
2.7 Sensor Installation
Various types (P/N’s) of sensors can be provided with the Model 610A Controller.
However, the installation method is identical in all cases. Please refer to Section 7.6.
The sensor assembly is used most often. It consists of P/N 10001-1 or 10058-1 sensor
plus GMI P/N 10252-1 Sensor Housing.
This assembly (P/N 10001-1 or 10058-1 + P/N 10252-1) is FM and CSA approved for
NEC Class I, Division 1 and Division 2, Groups B, C and D hazardous areas.
Each sensor assembly is connected to the controller using 3-conductor stranded cable,
and must be installed with conduit in hazardous areas. Total loop-resistance, ex cl uding
the sensor, must not exceed 40 Ohms. A separate cable is required for each sensor.
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